Jonathan's being such a Friend to All Children makes a whole lot of sense when you consider that, in his mortal life, he used to be a father.
In "I Was A Middle-Aged Werewolf," Mark hangs a lampshade on how much a young Michael Landon (in I Was a Teenage Werewolf) looks like Jonathan. Jonathan brushes it off as "I was never that young." Which is actually true, since when he was a young man, he was in a different body.
Also, Jonathan probably doesn't look in a mirror too much now that he's an angel. He's not vain; he almost certainly doesn't have to shower or shave; unless he's putting on a new set of clothes for an assignment, he really doesn't have much reason to pay attention to what his current body looks like. So of course he wouldn't notice the resemblance to a younger Michael Landon!
In "Song of the Wild West," Jonathan acts as if he knows the former owner of the club, Billy. He brushes it off as gambling being a common illness and "just having a feeling" that he knows what Billy would say, but given that Billy's deceased, it's entirely possible they do know each other!
